Question

quantos elementos tem a p.a FINITA [15,9,...,-81]

Answer 1

an=a1+(n-1).r

-81=15+(n-1).(-6)

-81=15-6n+6

-81=-6n+21

-6n=-81-21

-6n=-210 (-1)

6n=210

n=210/6

n=35